Liquid contact switch with auxiliary heating means



March 30, 1965 H. AWENDEFI ETAL 3,176,101

LIQUID CONTACT SWITCH WITH AUXILIARY HEATING MEANS Filed March 17. 1960 2 Sheets-Sheet 1 Fl 3 mvsurons Hans Awandor Erhard Becker Manfred Franks 8 Rudolf Enqel By I ll.

ATTORNEY March 30, 1965 H. AWENDER ETAL 3,176,101

LIQUID CONTACT SWITCH WITH AUXILIARY HEATING MEANS Filed March 17. 1960 2 Sheets-Sheet 2 r0 FIG.7. FI.G:-8. FIG.9.

as n 1 INVENTORS Hans A e der III Erhard egker Manfred Franks 8 ATTORNEY United States Patent O 3,176,101 LIQUID CONTACT SWITCH WITH AUXILIARY HEATING MEANS Hans Awender, Berlin-Nikolasse, Erhard Becker, Berlin- Lichtenrade, Manfred Franks, Berlin-Lankwitz, and Rudolf Engel, Berlin-Frohnan, Germany, assignors to Telefunken Aktiengesellschaft, Berlin, Germany Filed Mar. 17, 1960, Ser. No. 15,647 Claims priority, application Germany, Mar. 20, 1959, '1 16,431; Apr. 15, 1959, T 16,543 26 Claims. (Cl. 200-122) The present invention relates to a switch device and, more particularly, to a thermoelectric relay.

Various types of thermoelectric relays are known in the art and one such type, which is particularly used in the high frequency communication field, comprises a quantity of liquid metal, such as mercury, movable in an insulating tube which interconnects two gas chambers. When the temperatures in the chambers are equal, the metal will as sume an equilibrium position in which the pressures in the chambers are likewise equal. However, upon occurrence of a temperature difference in the two chambers, the pressure in one chamber will be greater than the pressure in the other chamber. As a result, the liquid metal moves to a new equilibrium position. utilized to open or close circuits between terminals positioned in the tube and insulated from each other. Such relay or switch may include an electrical heater for one chamber to produce the temperature difference. Such a switch can also be used to monitor thermo processes, in which case one of the gas chambers is heat conductively connected to the device to be monitored and the shifting of the liquid metal, due to a change in the temperature balance of the two chambers, causes a contact making or breaking.

In another known type of thermal relays, one of the chambers is under the influence of sun radiation and changes its temperature balance with the appearance and disappearance of the sun. Such an arrangement is shown, for example, in German Patent No. 892,793.

German Patent No. 1,008,412 discloses a thermo relay with two gas chambers which are heated by electric coils. Mercury gas switches of the above type have the disadvantage that the pressure increases faster than it decreases. In other words, the heating of the gas is carried out faster than the cooling oif, said cooling being achieved by turning oh the heating source. Therefore, such switch is relatively fast for the mode of switching initiated when the heat is turned on in one chamber, for example, for contact making, but slow in this case for contact breaking, because the mercury moves fast after the heat has been turned on, but slowly after the heat has been turned ofi.

To remedy this disadvantage, it is known to provide slow-acting pressure equalizing means between these two chambers. However, this measure is effective only if the second switching action is carried out soon after the initial one.

In German Patent No. 383,687, a switch is described having a membrane which is placed under tension when the gas is heated in one chamber. The membrane causes a fast return of the mercury when the heating is turned off. This device, however, has the distadvantage that the initial response of the switch is decreased because the gas has to be heated higher than usual before the first switching action associated with the initiation of the heating, can be carried out. Thus, while a speedier response for the switching action is obtained when the heater is turned off, this result is achieved at the cost of a reduced rate of response when the heater is turned on.

It is, therefore, an object of the present invention to overcome the deficiencies outlined above and to provide an This movement may be 3,176,191 Patented Mar. 30, 1965 improved thermoelectric switch, the response of which is very fast when the heating is turned off.

It is another object of the invention to provide a new and improved thermoelectric switch or relay in which the response for action when the heat is turned 01f is increased without reducing the response for action when the heat is turned on.

It is a further object of the invention to provide a new and improved thermoelectric switch or relay having a fast response when the heat is turned on or off.

It is a still further object of the invention to provide a new thermoelectric relay with automatic reset after a single initial control action.

With the above objects in view, the present invention resides mainly in a thermoelectric switching device which comprises means forming two chambers and a conduit interconnecting these chambers, stationary electrical contact means in said conduit, a liquid metal contact element arranged in the conduit and movable therein under the influence of the pressures prevailing in the chambers to cooperate with the contact means, means for applying heat to one of the chambers, and heat-conductive means interconnecting the chambers for at least partly equalizing the temperatures of the chambers when heat is applied to the one chamber for a prolonged period of time.

According to one aspect of the invention, in a pre ferred embodiment thereof, there is provided a housing having two gas filled chambers interconnected by a capillary containing an electrically conductive liquid drop and at least two contact terminals which may be interconnected by the liquid. A heater is provided for heating the gas in one of the chambers; another heater for heating the wall around the other chamber, whereby the gas is heated only indirectly. This second heater may be either a separate heating element or a heat conductor transporting heat from the wall around the first chamber to the wall of the second chamber.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a cross section through a light-sensitive thermoelectric relay according to a first embodiment of the invention.

FIGURE 2 is a cross section through a modified thermoelectric relay;

FIGURE 2a is a section along line 1-1 of FIG- URE 2;

FIGURE 2b is a section along line 22 of FIG- URE 2;

FIGURE 3 is a schematic diagram of the temperature distribution along the housing of the relay shown in FIGURE 2;

FIGURE 4 is another example of a thermoelectric switch according to the invention;

FIGURE 5 is a schematic cross section through a structure combining a plurality of relays according to the invention;

FIGURE 6 is a cross section of another embodiment of the invention;

FIGURES 7, 8 and 9 are modifications of a portion of a relay according to FIGURE 6, and

FIGURE 10 is a cross section of a further embodiment of the invention.

Referring in detail to the drawings, FIGURE 1 shows a glass member 1 comprising a capillary conduit 1a terminating at its ends in hollow spherical chambers 1b and 10. A contact element in the form of a mercury drop 2 is movably positioned inside of the conduit 1a. The spherical chambers 1b and 1c are filled with gas acting on both sides of the mercury. The mercury drop will 3 move into an equilibrium position to balance any pressure difference in the two chambers.

Two contact wires 3 and. 4 are sealed into the wall of the conduit 1a and at their lower ends form terminals 3 and 4 whiclrmay be contacted by themercury to close an electrical circuit, which includesthe. wires as well as a yoltage sourceflyand an indicator 10.

In the position shown in FIGURE 1, the mercury drop 2 engagesonlythe contact wire 4 atterminal 4? and, therefore, the circuit is open. A collector lens 5 directs the radiation 5' of a light source, which may,- for example, be

the sun, on a receptor, 6. positioned in the center of the chamber 111. The inner wall of this chamber is partially coated with a mirroring metal coating 7 and awindow 7a, this windowpermitting entry of thelight into .the chamber 1b.

Normally, no temperature difference is present between the two chambers 1b and; 1c, and between'thegas in the two chambers. If the samegas is used, more ga is ini- .tially filled in the chamber than .in the chamber 112,

.whereby the pressure .balanceshifts the mercury drop 2 la as well as the chamber'lc but, since there are no special radiation absorbers provided, the conduit 1a and chamber 1c willwarm up .very slowly as compared to the chamber 1b which is heated considerably faster and to a higher temperature ;due to the heating action of the receptor this receptor: being in direct contact with the gas and-thus heating it directly. The pressure in the chamber 1b increases so that the pressure balance of .the two chambers is brought out of equilibrium moving the mercury towards the left into a new equilibrium position. In this new position, the mercury establishes aconductive circuit between contacts 3 and 4.

If the radiation continues to impinge on receptor-6, the gas as well as the walls of the chamber 112 are heated as the gas has a small heat capacity and increases in temperature very rapidly, t hereby transporting heat to the wall and increasing its temperature. When the radiation terminates, the heating of the gas ceases. However, the gas does not cool rapidly, because a considerable amount of heat is stored in the glass wallof the chamber 112, this wall having a relatively high heat capacity. Thus, the mercury returns only very slowly .to its original equilibrium position. In other words, the circuit breaking is carried out considerably slower than the circuit making at the beginning of the heating.

The action described thus far is that which would take place if the switch were to incorporate no other structure. According to the present invention, however, there is an additional element which may be called a heat bridge 8, interconnecting ,the walls of the chambers 1b and 10. This heat bridge 8 comprises a metal bar having two calotte-shapedpans receiving a portion of the outer surface of the chambers 1b and 1c in matched relationship toprovide for alarge heat transport contact. The purpose of the heatbridge 8 is to convey heat from thewall of chamber lb to the wall of chamber 10. This heat conduction does, of course, not commence immediately after the radiation becomes effective, but will start only after the wall of chamber 1b is already heated by the conduction of heat from receptor 6 through the surrounding gas. After the Walls of chamber 1b are heated up, heat will flow rapidly through bridge 8 to the wall of chamberlc and thereby heat it. By thisheating, the device is made ready for the contact breaking step 11, 12 and 13 arenot present.

prior to initiation, as the gas in the chamber is is also being heated to a certain extent by heat conduction through the Walls. Of course, as long as the radiation is effective, there will always be a sufiicient temperature difference between the walls of the two chambers and the gas in the two chambers to maintain the drop 2 in its circuit closing position, i.e., the fiowof heat from chamber 1b to chamber 10 must not be so rapid as almost to equalize the temperature, because the mercury drop 2 would then be driven too much to the right to open the circuit, even though the radiation is still effective. If the radiation and, therefore, the heating cease, a temperature equalization between the two chambers 1b and 1c becomes effective very rapidly and the mercury drop 2 will open the circuit very soon aftertermination of the heating.

FIGURE 2 illustrates the application of the invention to a gas pressure thermoelectric relay comprising a glass member 21 having a capillary conduit 21a, a large gas chamber 211) and a small gas chamber 210. The conduit 21a contains a mercury drop 22 and communicates with chambers 21b and 210. A heating filament 29 is positioned in chamber 21b and is electrically connected to a voltage source 26 via a switch 25. Filament 29 heats the surrounding gas in chamber 21b. Contact Wires 23 and 24 terminate in the capillary-21a. The chambers 21b and 21care received in clamping rings 11 and 12, respectively, said rings being interconnected by a bar 13. Elements 11 to 13, preferably, are made of a heat conductive metal. Bar 13 is soldered or welded to rings 11 and 12 and these parts, together, from a heat bridge.

The operation of this anrangement as shown in FIG- URE 2 is basically similar to that shown in FIGURE 1. if the switch 25 is closed, the filament 29 heats the gas in chamber 2112, the mercury drop 22 moves to the left interconnecting wires 23 and 24. Some time after this circuit has been closed, the Wall of chamber 21b absorbs a certain amount of heat, a part of which will flow through ring 11, bar 13 to ring 12, thus heating the wall of chamher 210 and the gas therein, but does not heat sufiiciently to drive the mercury drop 22 to its initial contact opening position. After the heating of the filament,-the temperature equalization of the two chambers 21b and 210 is quickly obtained, due to the heat bridge 11, 12, 13 and the drop 22 moves to open the electrical connection of the contacts.

In FIGURE 3, the curve a indicates the normal temperature distribution of glass member 21 if the elements The glass wall of the chamber 21b reaches a considerably higher temperature than the remainder of the member 21 and, particularly, the glass wall of chamber 21c thereof.

The curve b shows how the temperature distribution is modified if the heat bridge 11, 12 and 1.3 is used. In this case, a certain amount of heat travels across this bridge and the clamping ring 12 to chamber 21c. Clamping ring .12 serves as an additional heat source for producing the temperature distribution as shown in curve [2.

The combined curves a and b denote the overall temperature distribution as produced by the entirearrangement shown in FIGURE 2. It will be seen from the curves, that the wall temperature of chamber 21c is only .a little less than the wall temperature of chamber 21b. The gas temperature in the chambers will 'diiter to a slightlyhigher degree, because in chamber 2112, the wall is-heated after the heat has traveled through the gas, ,while in chamber 210, the gas is heated from the wall. Thismeans that the gas in chamber 211') is warmer than its surrounding wall, while in chamber 21c,.the reverse holds true. This ensures that, as long as filament Z9 heats the gas incharnber 21b, the-mercury drop 22 will remain inits circuit closing equilibrium position. However,,this balance is a delicate one and as-soonas the filament lhstopsheating the surroundinggas, the chamhers quickly tend to assume similar temperatures and mercury drop 22 will move quickly to the right, to thereby interrupt the electrical connection between wires 23 and 24. The contact breaking is carried out almost as fast as the contact making at which time the filament 29 was connected to a heating source.

The device shown in FIGURE 4 comprises a cylindrical glass member 41 having a capillary conduit 41a interconnecting a larger gas chamber 41:; and a smaller gas chamber 41c. Within the chamber 41b, there is a heating filament 45. A mercury drop 42 moves in conduit 41a and one of a pair of contact wires 43 is led through chamber 410 and terminates in the conduit 410 wh le the other wire 44 is led directly into the conduit 41a. A heat bridge is provided formed by a simple metal strip 48 and extending along the outside member 41. A cylinder 46 encompasses the entire arrangement and assists the heat conduction in and along heat bridge 43. The cylinder 46 may be made of a suitable synthetic or plastic material. The space between cylinder 46 and member 41 may be filled with plastic material or any other kind of synthetic material. Alternatively, cylinder 46 can be made of a heat-conductive synthetic and can be of such size that it touches the entire surface of member 41. In this case, the cylinder would take over the function of the special heat bridge 43 which, then, could be omitted.

The cylinder 46 may serve as a protective cylinder so that the gas pressure in the chambers can be selected very high, for example, 2 to 30 atmospheres. In this case, the cylinder serves as a protective shield to prevent, in case of breakage, glass splinters from scattering.

In FIGURE 5, a honeycomb arrangement is illustrated, incorporating a plurality of switches of the type shown in FIGURES l, 2 and 4. In such an arrangement, the protective shields, such as 46 in FIGURE 4, of several relays can be combined into a single housing 14 having the desired number of cells for receiving the various relays. Such an arrangement is of advantage if a number of relays are used in an electrical apparatus. In practice, it may be of advantage to provide more cells than the number of cells actually used, in order to have some spare cells which, at first, remain empty, but will receive other relays to be used in case of repair of the ones in use.

The cells of the housing 14, shown in FIGURE 5, are shown in rectangular cross section, however, other cross sections, such as a hexagonal one, may also be used.

The examples of the invention described above show two contacts only to be opened or closed. It will be understood, however, that more than one contact may be positioned in the path of the mercury drop moving in the conduit. Such contact may, for example, be used to open and close circuits in a predetermined sequence.

The design of the relays shown in FIGURES 2 and 4 is selected to reduce the increase of the capacitance of contacts 23 and 24 (FIGURE 2) and 43 and 4-4 (FIG- URE 4) relative to ground, said capacitance increase being due to the influence of the metallic heat bridges. Thus, the thermo relays as described are still suitable as switches in high frequency circuits. The heat bridge is designed to operate with only a minimum or mass of material and is positioned as far away from the contact wires as possible. However, if the switches are to be used in DC. or low frequency AC. circuits, the bridge can be enlarged, i.e., more metallic material can be brought into heat or thermo contact with the glass body of the relay, regardless of the proximity of the contact wires. The heat bridge can, for example, be produced by depositing a metallic layer on the glass member so that only a certain area around the lead in wires is kept free from the metallic deposit in order to avoid short circuits.

Another modification is posisble in placing the glass member of the relay singly or combined with others in a compact metallic housing. According to a further modification, it is possible to submerge the glass member of the relay, singly or combined with other relays, into a heat-conductive fluid. If the dielectric constant of this fluid is suficiently small, this arrangement can also be used in high frequency circuits. If the viscosity of such fluid is small, the relays are placed in a vertical position, so that the chamber containing the heating element is at the bottom. An additional heat transport is then produced, due to the how of convection heat in the fluid along the relay member.

The embodiments of the invention described thus far use heat conduction from a primarily heated chamber to another chamber which is positioned on the other side of the mercury drop to be moved by pressure difference prevailing in the chambers. It is, of course, inevitable that this heat conduction operates with some delay. This delay is not important if the switching intervals are relatively large, i.e., if the switch will remain in a closed position for any length of time, it does not matter that some time will elapse before the relay is prepared for a fast circuit breaking action after the heating has been turned otf.

FIGURE 6 illustrates a modified embodiment of the invention in which, for all practical purposes, the abovediscussed delay is avoided. The glass member 61 corresponds to member 1 in FIGURE 2 and has a large gas chamber 61b and a capillary conduit 61a connecting chamber 61b to a small gas chamber 61c. A heating filament 69 is housed in chamber 61b and is electrically connected to two lead-in terminals 65 and 66 which are electrically connected to terminals 73, 72, respectively of a voltage source. Chamber 61b could also be called an expansion chamber and chamber 61c could be called a compression chamber because of the expansion and compression, respectively, produced when the switch is turned on. A mercury drop 62 is movably arranged in conduit 61a and is adapted to interconnect electrically two contact wires 63 and 64.

The compression chamber 61c is heat-conductively connected to a heating coil 68 having the form of a cylindcr which may be slid upon the outside of chamber 61c. Heating coil 68 may be embedded in a ceramic support. Numerals 67 and 7% denote the electrical connections of heating coil 68 and voltage source terminals 72 and 73, respectively. A potentiometer 71 is inserted in connection line 67 to adjust the heating current. A switch 74 governs the current supply to both heating coil 68 and filament 69. If the switch 74 is closed, electric heating current is simultaneously supplied to the two heating elements 6% and 69. Filament 69 is positioned inside or" the chamber 612: and, therefore, its heating effect acts upon the gas therein immediately before any heat can be absorbed by any part of the wall of the glass member 61. Thus, the mercury drop 62 moves quickly towards the left side of the conduit 61a and interconnects the wires 63 and 64. The coil 68 does not heat the gas in chamber 61c directly, but does heat the wall of this chamber. The relative proportion of heating of the two chambers in adjustable by resistor 71 which, preferably, is set in a position wherein the walls of the two chambers are heated to an approximately equal temperature. This, however, means that the wall of the chamber 61b is heated indirectly by heat conduction through the gas and the wall of the chamber 610 is heated directly. When a new equilibrium condition is established, the distinctions between it and the original equilibrium condition, correspondng to open circuit position, are twofold. First,

' the overall temperature of the member 61 is higher than that of the environment. Second, the gas in chamber 61b is directly subjected to the heating of the heating filament 69 and, therefore, this gas has a higher temperature than any other portion of the relay, including the walls of the two chambers which have approximately equal temperature, as well as the gas in chamber 61c having a temperature slightly below the wall temperature. On the other hand, it will be observed that the preparation of the relay for turn off is started immediately after the heating current is turned off. Thus, the relay is very quickly made ready for a fast turn off, which means that the time interval during which the mercury bridges the contacts can be quite small. When the switch 74 is opened, the direct heating of the gas in chamber'dlb is interrupted, thereby disturbing the pressure balance of the two chambers. The mercury is returned almost immediately to its original equilibrium position, whereby the electrical connection of wires 63 and 64 is opened. Due to the fact that the walls of the chambers are of approximately equal temperature at the moment the heating current is turned off, there is no time delay during which any heat transport takes place. This is so, because the removal of the heating effect of the filament 69 immediately affects the pressure balance of the two gas chambers.

A further increase of the turn-off speed of this switching device can be produced by adjusting the heating of coil 68 to such an extent that the static temperature distribution during a closed circuit results in a smaller leftward deflection of the mercury drop from its resting position than the initial deflection produced immediately after switch 74 was closed, i.e., after filament 69 was permitted to heat the surrounding gas. This adjustment is regarded to be the optimum adjustment producing minimum delay of turn off.

In a modification of the adjustment of resistor 71, it is possible to produce a monostable oscillator or a switch which automatically turns off after a predetermined period of time. To achieve this result, the heating current for coil 68 is adjusted to heat chamber 610 and the gas therein to a higher temperature than filament 69 heats the gas in chamber 61b. However, the heating of the gas in chamber 610 is delayed, as compared with the heating or" the gas in chamber 611). Thus, upon closing of the switch '74, the filament 69 will first heat its surrounding gas to drive mercury drop 62 towards the left to make the connection between wires 63 and .64. The heating of wall 68, even though started simultaneously, affects the gas in chamber 61c only after some delay, but after a certain period of time, this .gas will have the same or a higher temperature than the gas in chamber 61b, whereafter the mercury drop 62 will be driven back to open the contacts. Such a switch can be used in control circuits where it is desirable to have an initial switching effect terminated automatically without additional command signals.

From the foregoing, it is apparent that resistor 71 serves as a fine adjustment means for various and accurate modes of operation of the relay. If one particular relay is to be used for one given mode of operation only, resistor 71 may structurally be combined with the member 61. For example, a particular resistive substance may be deposited as a strip on the outer surface of member 61 and may be electrically connected at one side with one terminal of coil 68. Then a test is made as to how much resistance is needed to produce a particular current in coil as for the mode of operation desired and the remainder of the deposit is scraped away. The resistive strip is then connected to a line which, in turn, is connected to the voltage source feeding coil 68.

FIGURE 7 illustrates an arrangement wherein the heating coil 68 is wound directly on the outside of chamber 610.

FIGURE 8 showsan arrangement wherein the heating coil 68" is positioned somewhat removed from the outer surface of chamber 610. Here, chamber 610 is primarily heated by radiation.

The relay, as shown'in FIGURE 6, can also be used together with other relays of similar type and these relays can be arranged as indicated above with reference to FIGURE 5. The housing, such as 14 in FiGURE 5, may be provided with the heating coils shown in FIGURES 6 to 8, and the electrical connections to these heating coils are attached to the housing into which the various relays are placed. One resistor may serve to adjust all the heating currents, which resistor may, likewise, be housed in housing 14. The contacts and connections corresponding to 63 to 5 remain the same as in the single relay.

Finally, it should be noted that it is possible to combine in one relay the heat bridge shown in FIGURES 1, 2 and 4, and an auxiliary coil, such as shown in FlGURE 6. Such an arrangement is illustrated in FIGURE 10. in this case, a very wide range of circuit breaking delay is obtained, as measured from the opening of the heating circuit for the filament until the opening of the circuit. Thus, FIGURE 10 shows a glass member 81 which is provided with a large gas-filled chamber 8112, a small gas-filled chamber 810 and a capillary conduit 81a interconnecting the two chambers. A heating filament 89 is positioned inside of the large chamber 8117, said heating filament connecting to a voltage source 91. A mercury drop'SZ moves in the conduit 81a, and the contact wires 83 and 8d terminate adjacent chamber 81c within reach of mercury drop 82. A heating coil 88 is mounted outside of but adjacent to chamber 810 on a protective cover 90. Coil 38 is electrically connected to the voltage source 91 through lines 36, a switch 94 and a potentiometer 87. The application of the voltage from source 91 to both filament 89 and coil 83 is controlled by a switch 92. A heat bridge 93 made of metal heat-conductively interconnects the walls of chambers 31b and 810. When switch 94 is closed, the temperature of chamber 31c is primarily determined by the heating action of coil 38 acting faster than the heat transport through bridge 93. If switch 94 is open, the temperature of chamber 810 is only determined by the heat transport through bridge 93.

it should be observed that in all examples of the present invention as described above, the open and closed positions of the liquid drop may be reversed, i.e., the wires may be so placed that the drop closes the contact when the heater in the first chamber, designated by numeral with the sufiix b, is turned off, but opens the contact when this heater is turned on.

We claim:

1. A thermo relay comprising; a first gas-filled chamber, a second gas-filled chamber, a conduit interconnecting said two chambers; two electrical conductors in said conduit insulated from each other; an electrically conductive liquid drop in said conduit movable therein for interconnecting said two conductors; heat generating means positioned in said first chamber; and means located exteriorly of said second chamber and connected with said first chamber for heating the wall of said second chamber from the outside thereof.

2. A thermo relay comprising: a first gas-filled chamber; a second gas-filled chamber; a capillary interconnecting said two chambers; contact terminals positioned in said capillary; an electrically conductive liquid drop in said capillary adapted to interconnect and to disconnect said terminals; heat generating means positioned in said first chamber; and means located exteriorly of said second chamber and connected with said first chamber for heating the wall of said second chamber delayed with respect to the heating as efiective in said chamber.

3. A thermo relay comprising: a first gas-filled chamber having walls; a second gas-filled chamber having walls; a capillary interconnecting said two chambers; contact terminals positioned in said capillary; a drop of conductive liquid in said capillary for interconnecting and disconnecting said terminals; power means for producing heat inside of said first gas chamber at a point spaced from said wall thereof; and means deriving its energy from said power means and located exteriorly of and adjacent the wall of said second chamber for heating the same.

4. A thermo relay comprising: a first gas-filled chamber having walls; a second gas-filled chamber having walls; a capillary interconnecting said two chambers; contact terminals positioned in said capillary; an electrically conductive liquid contact element in said capillary for interconnecting and disconnecting said terminals; a heat source in said first chamber for directly heating the gas therein; and adjustable means connected with said first chamber, being located exteriorly of said second chamber, and elfective on a wall of said second chamber for heating said wall and therefore the gas in said second chamber.

5. A thermo relay comprising an insulated housing having two gas-filled chambers and a conduit interconnecting said two chambers; contact terminals positioned in said conduits; a mercury drop movably positioned in said conduit for electrically interconnecting and disconnecting said terminals; a heat source in one of said chambers for directly heating the gas therein; and heat-conductive means located exteriorly of said chambers and interconnecting the portion of the housing adjacent said one chamber and another portion of the housing adjacent the other of said chambers.

6. A thermo relay as set forth in claim 5, said heatconductive means comprising a metallic bar heat-conductively connected to said housing and in contact therewith at least adjacent said two chambers.

7. A thermo relay as set forth in claim 5, said heatconductive means comprising: a first metal ring encompassing said housing adjacent one of said chambers; a second metal ring encompassing said housing adjacent the other of said chambers, and a strip-shaped heat conductor interconnecting said two rings.

8. A thermo relay as set forth in claim 5, said heat conductive means further comprising a protective cover enclosing said housing.

9. A thermo relay as set forth in claim 8, said protective cover comprising a tube and a synthetic material filler in the space between said housing and said tube.

10. A thermo relay comprising: a first gas-filled chamher; a second gas-filled chamber; a conduit interconnecting said two chambers; contact terminals positioned in said conduit; an electrically-conductive liquid contact element in said conduit for interconnecting and disconnecting said terminals; a first heat source in said first chamber for di-- rectly heating the gas therein; and a second heat source exteriorly of said second chamber and connected with said first heat source for heating at least a portion of the wall of said second chamber and therefore the gas in said second chamber.

11. A thermo relay as set forth in claim 10, further comprising power supply means and switching means for substantially simultaneously connecting said heat sources to said power supply means.

12. A thermo relay comprising a housing having a first and a second gas-filled chamber and a conduit interconnecting said two chambers; contact terminals positioned in said conduit; a mercury drop in said conduit for interconecting and disconnecting said terminals; a first electrical heater including a filament positioned inside said first chamber and contacting the gas therein; means for supplying electric current to said first heater; a second electrical heater operatively associated with said first heater for heating the wall of said housing and arranged adjacent said second chamber, the gas in said second chamber therefore being heated only by heat conduction through its adjacent walls; and means for supplying electric current to said second heater.

13. A thermo relay as set forth in claim 12, said lastmentioned means including a potentiometer.

14. A thermo relay as set forth in claim 12, including switching means for simultaneously controlling the current supply to said first and said second heater.

15. A thermo relay as set forth in claim 12, said second heater comprising a coil wound on said housing adjacent said second chamber.

16. A thermo relay as set forth in claim 12, said second heater comprising a coil embedded in the housing adjacent said second chamber.

17. A thermo relay as set forth in claim 12, said second heater comprising a coil receiving said housing in spaced relationship therewith, adjacent said second chamber.

18. A thermo relay as set forth in claim 12, further comprising a protective cover surrounding said housing, said second heater being mounted on said cover adjacent said second chamber.

19. A thermo relay comprising: a housing having a first and a second gas-filled chamber anda capillary interconnecting said two chambers; contact terminals positioned in said capillary; a liquid drop in said capillary; first heater means for directly heating the gas in said first chamber and thereby increasing the pressure therein, whereby the liquid drop is deflected from its normal position into a second position; and second heater means connected with said first heater means for indirectly heating the gas in said second chamber by heat conduction through its adjacent housing portion and thereby increasing the pressure therein, whereby said deflection of said liquid drop is at least partially cancelled and said drop is moved into a third position.

20. A thermo relay as set forth in claim 19, wherein said drop, when in its second or third position, electrically interconnects said terminals and, when in its normal position, disconnects said terminals.

21. A thermo relay as set forth in claim 19, wherein said drop, when in its second position, electrically interconnects said terminals and, when in its third or normal position, disconnects said terminals.

22. A thermoelectric switching device comprising: wall means forming two gas chambers and a conduit interconnecting said chambers; stationary electrical contact means in said conduit; a liquid metal contact element arranged in said conduit and movable therein under the infiuence of the pressure prevailing in said chambers to cooperate with said contact means; means for applying heat to at least one of said chambers; and heat-conductive means located exteriorly of and interconnecting said chambers for at least partly equalizing the temperatures of the wall means forming said chambers when heat is applied to said one chamber for a prolonged period.

23. A thermoelectric relay comprising: a housing having a first and a second gas-filled chamber and a capillary interconnecting said two chambers; contact terminals positioned in said capillary; a liquid drop arranged in said capillary for movement between a normal position, a first operating position wherein said terminals are electrically connected, and a second operating position wherein said terminals are disconnected; first heater means in said first chamber for heating the gas therein and thereby moving said drop from its normal position to one of said operating positions, the walls of said first chamber being heated by conduction through the gas therein; and second heater means located exteriorly of said second chamber and effective substantially simultaneously as said first heater means for heating the wall of said second chamber from the outside thereof to substantially the same temperature as the walls of said first chamber, whereby the gas of said second chamber is heated by conduction moving said drop into the other of said operating positions.

24. A light-sensitive switching device comprising: a first and a second gas-filled chamber, said first chamber having a transparent wall portion; a capillary interconnecting said chambers; a liquid drop of electrically-conductive material positioned in said capillary; contact terminals in said capillary interconnectable by said drop positioned therein; a light-absorbing receptor in said first chamber adjacent said transparent wall portion; and heatconductive means located exteriorly of and heat-conductively inter-connecting the Walls of said two chambers.

25. A thermo relay comprising: a housing having two gas-filled chambers and a capillary interconnecting said chambers; a liquid drop or" electrically-conductive material in said capillary; a pair of contact terminals in said capillary; a first heater element in said first chamber for heating the gas therein; means for heat-conductively interconnecting the walls of the two chambers; and an additional heat source located exteriorly of said second chamber for supplying heat to the wall of said second chamber, from the outside thereof, whenever heat is produced inside of said first chamber.

26. A thermo relay as set forth in claim 25, said additional heat source being selectively disconnectable from a power supply therefor.

References Cited in the tile of this patent UNITED STATES PATENTS Parks et a1 July 7, 1936 Hermeyer Aug. 27, 1963 FOREIGN PATENTS Denmark May 18, 1948 Italy Jan. 15, 1931 Germany Sept. 13, 1917 Great Britain Feb. 27, 1939 nce Sept. 26, 1924 France May 4, 1934 

1. A THERMO RELAY COMPRISING; A FIRST GAS-FILLED CHAMBER, A SECOND GAS-FILLED CHAMBER, A CONDUIT INTERCONNECTING SAID TWO CHAMBERS; TWO ELECTRICAL CONDUCTORS IN SAID CONDUIT INSULATED FROM EACH OTHER; AN ELECTRICALLY CONDUCTIVE LIQUID DROP IN SAID CONDUIT MOVABLE THEREIN FOR INTERCONNECTING SAID TWO CONDUCTORS; HEAT GENERATING MEANS POSITIONED IN SAID FIRST CHAMBER; AND MEANS LOCATED EXTERIORLY OF SAID SECOND CHAMBER AND CONNECTED WITH SAID FIRST CHAMBER FOR HEATING THE WALL OF SAID SECOND CHAMBER FROM THE OUTSIDE THEREOF. 